Abstract
Purpose: :
Human retinal pigment epithelial cells (hRPE) have been shown to play a role in the pathogenesis of proliferative eye diseases. In addition, insulin therapy has been associated with transient worsening of proliferative diabetic retinopathy. Since Vascular Endothelial Growth Factor (VEGF) and Fibroblast Growth Factor 2 (FGF2) have been shown to be angiogenic and the Somatostatin receptor subtype 2 (sst2) to be anti-angiogenic, we investigated the synthesis of VEGF, FGF2 and sst2 on hRPE cells in presence of insulin.
Methods: :
Primary hRPE cell cultures were established from human eyes obtained from the Michigan Eye Bank. Cell proliferation was determined by the trypan blue exclusion method (T) and 3H-thymidine incorporation (3H-thy). VEGF, FGF2 and sst2 synthesis were quantitated by immuno-precipitation with 14C-methionine labeled VEGF-, FGF2- and sst2- specific antibodies and localized by immuno-histochemical studies. Data were analyzed by Student 't' test.
Results: :
Insulin (0-5 µg/ml) stimulateed hRPE cell proliferation in a dose dependent manner as determined by T and 3H-thy. Insulin (0-5 µg/ml) also stimulated 14C-methionine-VEGF synthesis (3798±727 vs. 2726±598, CPM±SEM, n=4, p ≤ 0.05) and 14C-methionine-FGF2 synthesis (758.3±214.4 vs. 480.91±154.0, n=5,p≤0.05 ) synthesis in hRPE cells, also in a dose dependent manner. However, insulin had no effect on 14C sst2 synthesis (1386±650 vs. 1251± 611, CPM±SEM, n=4,p≥0.05) in these cells. Immuno-histochemical studies confirmed increased immuno-reactivity of VEGF and FGF2 but not sst2 in hRPE cells exposed to insulin.
Conclusions: :
Insulin stimulates hRPE cell proliferation, possibly by stimulating synthesis of the angiogenic factors VEGF and FGF2. However, insulin has no effect on synthesis of the anti-angiogenic factor, sst2. These findings may help to explain the worsening effect on proliferative diabetic retinopathy sometimes associated with insulin.
Keywords: diabetic retinopathy • retinal pigment epithelium • drug toxicity/drug effects